No Load, Higher RPM break up crackiling

[Diamond Back]

I purchased a Silver Flying Horse Kit from Gas Bikes .. I believe it is a GT5 38mm stroke motor. I know there are a lot of different kits out there,, like PK80, 40mm stroke, 2 different pistons and 5-6 connecting rods out there,,, I seem to have the 38mm smaller piston and no marking copper color rod,, I would like to say that my cylinder was in good quality,, barely any casting flaws.

I have the slant head with spark plug towards rear of engine.
stock NT carb with needle clip in 2nd down from top out of 5 positions, the first carb they sent had all chinese markings on it and a 4 position needle, they sent me a new one cause plastic float leaked, new one has slight differences like 5 postion needle and different looking main jet.. I know that these carbs have a way to big.079 main jets and that can cause 4-stroking
I have a banana type expansion pipe,
stock cdi and magneto in 1 oclock postion and ohms out at 320
spark plug boot real crappy and has like this loose spring clip inside it,,, dont like it but get spark
tried all types of different spark plugs ,, no difference
running 32 to 1 synthetic mineral 2 stroke Bel Ray oil..
tried adjusting needle clip posistions,,, a little better a low throttle and rpms
i port matched the exhaust pipe flange to be more oval then small round
trimmed base gasket where there was overlapping but have not case matched to jug or done anything with intake except add o-ring to prevent leaking
bike has real good compression and lots of power,,, i never have to pedal,,, and starts right up even with out choke,,, never used choke yet
i live in Stroudsburg PA, and probably a little high here in elevation
**** Like I said,, when starting off under load and throttle it purrs good and smooth, as soon as it starts to rev up like when the pipe should be kicking in some powerband it just starts to break up and crackle and loose power and at 15-20mph half throttle no load cruising it does the same crackiling and popping.

and also what should i do with my dremel and light porting,, like i can see a good bit of piston in exhaust port a BDC which also means my transfer ports arent getting un covered all the way either,, and the intake is all overlapping and can see piston skirt at TDC.. and bottom case to cylinder jug transfers is also all overlapping not matched metal... please help as i read and hear all types of things to do and everyone says he or he is wrong ... confusing... just want it to run smooth from low to high and feel a powerband kick at like 5000 rpms... I think if i port matched everything and smooth the flow out thru engine should run better,,, dont know what to do about piston skirt on intake side and raise exhaust port a little,,, or use thick base gasket and sand down head ???? also should i just adapt a Walboro 15mm carb and adjust hi and low speed settings like on my 50cc scooter... please help








i

 

[Diamond Back]

 

[HeadSmess]

sounds too rich, especially if you arent needing the choke. i had one particular engine, would take 50 metres to even pop, a few hundred metres to warm up...then off it went like a scalded cat. engines tend to get "richer" when warm.

the piston never completely clears the exhaust port, thats a 66cc design flaw... they always cleared on the 48's.

dont play around with the port timings unless you know what you are doing or have replacement parts for the steep learning curve that follows.

go wider on ports rather than higher, remembering to keep tops of ports curved for ring-life, and not getting too close to the ring-gaps.

matching transfers/ports does help but not much, these engines all suffer from asthma... mainly on the intake. notching the piston to clear the port at TDC helps but theres a fine line between enough and too much. once again, the wider you can get it, the better...

 

[crassius]

I like the clone carb with chinese markings (never had to adjust one in the couple years I've been selling them) - first thing you should do is put the new float in that carb and see what happens.

 

[Diamond Back]

i did put new float in and adjusted to 21mm... stop leaking,, but no difference in 4-stroking... i think i need to put a .064 main jet in,,, plus i got play-dough today and am going to case match bottom end ,, you put the play-dough in tightly so no metal shavings get in crank.... some one said to take a small copper wire thru the main jet and ball it on both ends so it dont fall thru and that should lean it out... i know you can solder and re-drill but i dont have solder or drill that small.... also said on the stock NT slide on back side it is slanted,,, the said you can sand down slant a little to lean it out... but that wont help WOT... only main jet does that.... do you have a main jet you can spare...i can mail you a few bucks if you want to help a veteran out

 

[Diamond Back]

sounds too rich, especially if you arent needing the choke. i had one particular engine, would take 50 metres to even pop, a few hundred metres to warm up...then off it went like a scalded cat. engines tend to get "richer" when warm.

the piston never completely clears the exhaust port, thats a 66cc design flaw... they always cleared on the 48's.

dont play around with the port timings unless you know what you are doing or have replacement parts for the steep learning curve that follows.

go wider on ports rather than higher, remembering to keep tops of ports curved for ring-life, and not getting too close to the ring-gaps.

matching transfers/ports does help but not much, these engines all suffer from asthma... mainly on the intake. notching the piston to clear the port at TDC helps but theres a fine line between enough and too much. once again, the wider you can get it, the better...

Thank you Buddy... i have owned and lived with 2 strokes my whole life,,,CR80, KX125, Fourtrax 250R atv's and trikes and 49cc scooters...so i am familiar.. do you know the 15mm walboros used on the 49cc chinese scooters,,, they are great with the high and low,,, i would have to make a custom intake and line up and drill hole for pulse hole right thru and under intake on cylinder.... do you know of an intake that may work or get me close... and is 15mm to small

 

[crassius]

before making permanent changes, I'd lower float level some to see if that is the direction to go - at 21mm your main should just be peeking thru float - bend prongs till it is just sunk in float & see what happens

 

[Diamond Back]

before making permanent changes, I'd lower float level some to see if that is the direction to go - at 21mm your main should just be peeking thru float - bend prongs till it is just sunk in float & see what happens

how does changing float hight help in running performance... that float just opens and closes the needle under fuel inlet to allow gas in the carb bowl and shuts it off when there is enough so it doesnt overflow out the back,,, what does it do by having low or high... dont get it,,, explain please

 

[HeadSmess]

the fuel sucks up through the jet via venturi action. the higher it has to lift the fuel, the harder it is... lower fuel level= leaner. you get a slight bit of adjustment using that trick. go to far and the jet starts clearing the fuel when you hit bumps... more prone to fuel frothing too...

the (super fine) wire through the jet works, dont ball the ends up cus they can block the jet, just tack one end to the base of the jet with some solder.

keep adding a wire at a time til you go to far then remove one.

sets of microdrills are cheap, but you do need a pin chuck for them... worst case, hold jet in a drill, hold the bit with pliers. you also need a 3mm to remove excess solder from the jet where its bored out. the length of jet orifice also affects the mixture... a short, small hole can flow just as much as a long fat hole, due to friction.


walbros are great, aim for an 18 though, lets you open the intake port up a tad.

some have external pulse feeds(usually on chainsaws), or you can simply drill/tap and add a nipple to the cover(or even the manifold), with another nipple on the crankcase somewhere convenient...

manifold for walbros should include some type of plasticy thing to prevent heat from getting to the carb, which causes vapor lock... why theyre always mounted on those nylon/epoxy manifolds.

only bad feature with them is getting the cable attached nicely if theyre standard butterfly types that normally run wire linkages.

also lets you stick the fuel tank anywhere

 

[Diamond Back]

the fuel sucks up through the jet via venturi action. the higher it has to lift the fuel, the harder it is... lower fuel level= leaner. you get a slight bit of adjustment using that trick. go to far and the jet starts clearing the fuel when you hit bumps... more prone to fuel frothing too...

the (super fine) wire through the jet works, dont ball the ends up cus they can block the jet, just tack one end to the base of the jet with some solder.

keep adding a wire at a time til you go to far then remove one.

sets of microdrills are cheap, but you do need a pin chuck for them... worst case, hold jet in a drill, hold the bit with pliers. you also need a 3mm to remove excess solder from the jet where its bored out. the length of jet orifice also affects the mixture... a short, small hole can flow just as much as a long fat hole, due to friction.


walbros are great, aim for an 18 though, lets you open the intake port up a tad.

some have external pulse feeds(usually on chainsaws), or you can simply drill/tap and add a nipple to the cover(or even the manifold), with another nipple on the crankcase somewhere convenient...

manifold for walbros should include some type of plasticy thing to prevent heat from getting to the carb, which causes vapor lock... why theyre always mounted on those nylon/epoxy manifolds.

only bad feature with them is getting the cable attached nicely if theyre standard butterfly types that normally run wire linkages.

also lets you stick the fuel tank anywhere

Thank you man,,, your a cool person to help me like this,,, you seem very smart so I going to ask you a few more questions,,,sorry, but i trust your input...what do you think of Banana pipe with out silencer?? is it a top end or bottom end pipe,,, would putting a small 2-3 inch header help.. maybe cause my bike dont run right now in high rpms,, but the bike has alot of power,, i never peddle,,, but i dont get that powerband nitrous effect like on my KX125,,, why is that...

Also should I widen a hair, not overdue it the exhaust port and intake port,,, also some say to raise exhaust port a hair and some say cut piston skirt on intake side just enough to be open at TDC... a guy just told me that he lost power doing this,,, what should i do..??? this is what I mean,,, one person says and does one thing,, and a nother guy says NO,, you will lose power,,, its so hard to get the truth and hard facts